1. Field of the Invention
The invention relates to a method of forming a carbon particle-containing film, which forms a film containing the composition of metal powder, a heat transfer member manufactured by the method, a power module, and a vehicle inverter and, more particularly, to a method of forming a carbon particle-containing film, which allows low-cost and easy film deposition, a heat transfer member, a power module, and a vehicle inverter.
2. Description of the Related Art
A power module (module) 90 used for a vehicle inverter, or the like, according to a related art is formed of electronic components shown in FIG. 9. Specifically, the power module 90 at least includes a power device 91, an insulating member (aluminum nitride material) 93, and a heat sink member 94. The power device 91 is formed of a silicon device. The insulating member 93 is made of aluminum nitride to which the power device 91 is fixed via a solder layer 92. The heat sink member 94 is made of aluminum. Furthermore, a buffer member 95 made of copper-molybdenum (Cu—Mo) or aluminum-silicon carbide (Al—SiC) is arranged between the insulating member 93 and the heat sink member 94. The buffer member 95 is used to not only transfer heat generated from the power device 91 to the heat sink member 94 to radiate the heat but also buffers a difference in thermal expansion between the insulating member 93 and the heat sink member 94. The buffer member 95 is fixed to the insulating member 93 by the solder layer 96, and is fixed to the heat sink member 94 by silicon grease 97. In this way, the buffer member 95 together with the heat sink member 94 constitutes a heat transfer member for radiating heat from the power device 91.
In order to improve radiation of heat from the power device 91, Japanese Patent Application Publication No. 2006-298687 (JP-A-2006-298687), for example, describes a method of making a heat transfer member contain carbon particles. When the above method is used to manufacture the buffer member 95, carbon particles are initially baked to be networked to thereby manufacture a porous sintered compact, and then metal is impregnated into the porous sintered compact.
However, even when the above buffer member is used, in the power module 90, the thermal conductivity of the silicon grease 97 that fixes the buffer member 95 is lower than those of the other members, so the silicon grease 97 becomes an obstacle to transferring heat of the power device 91 to the heat sink member 94.
To work around the above problem, for example, powder containing carbon particles may be directly sprayed to the surface of the heat sink member 94 to form the buffer member without using the silicon grease 97. However, during film deposition, when carbon particles are tried to be sprayed while metal is melted, the carbon particles are gasified by oxidation reaction and burned, so it is difficult to make the film contain carbon particles.
In view of the above, Japanese Patent Application Publication No. 2004-232035 (JP-A-2004-232035), for example, describes a method of forming a film as a buffer member by thermally spraying powder, formed of powder particles that graphite particles (carbon particles) are coated with metal films, to a base material. With the above film deposition method, only metal films are melted and then thermally sprayed, so it is possible to make a film contain carbon particles.
However, when the above film deposition method is used to form a film, it is necessary to manufacture carbon particles, of which the surfaces are plated with metal, and powder that contains carbon particles treated to be covered with metal during granulation. Then, if parts of surfaces of carbon particles are exposed, the exposed surfaces are caused to perform oxidation reaction during thermal spraying, so carbon particles may be possibly burned. In addition, it is desirable that the surfaces of carbon particles are completely coated with metal. However, powder made of particles manufactured by the above described method is considerably expensive, and it is not realistic to apply the powder to automobile components, or the like.